1. Field of the Invention
Embodiments of the present invention relate to methods and compositions to detect analytes in a sample using antibody molecules that are transformed into nanoscale “self-signaling” biosensors, in particular those methods and compositions that provide for single-step detection of target analytes without the need for labor-intensive steps necessary in conventional assays.
2. Description of the Related Art
Immunoassays are based on specific interactions between antibodies and antigens. They are indispensable in modern clinical diagnostics, drug screening practices, and medical research in general. Among the immunoassay formats, enzyme-linked immunosorbent assay (ELISA), lateral-flow immunoassays, and Western-blot assays are most widely used. ELISA and Western-blot techniques require multiple cycles of incubation/washing steps and are hence laborious and prone to operator error. Lateral-flow immunoassays, such as dip-stick type assays, generally provide faster detection but are not as sensitive or accurate as conventional ELISAs. All of these assays are conducted using the heterogeneous format, i.e. they all require immobilization of antibodies or antigens onto a solid surface. In comparison, homogeneous assays, in which no antibody/antigen immobilization is necessary, provide many important advantages over the heterogeneous assays. First and foremost, homogeneous immunoassays enable direct detection in solution, in a “mix and detect” manner, without needing multiple incubation steps or additional signal-generating elements, and hence greatly accelerate assay throughputs while preserving assay sensitivity and specificity. Furthermore, it is preferred to conduct the homogeneous assays in the non-competitive format as opposed to competitive format since the former is in general more sensitive by orders of magnitude [Ohiro et al. 2002, herein incorporated by reference in its entirety]. Having an effective and universal assay platform that allows homogeneous solution-phase non-competitive immunoassays is particularly valuable when interrogating a large number of samples since such format is more amenable to automation using robotic liquid-handling systems prevalent in modern high-throughput screening applications. However, a key technical challenge has been the development of a simple and effective reporting mechanism to signal the antigen-antibody interaction in solution.